1. Field
The disclosure relates to manuscript carrying apparatuses that take out sheet-by-sheet and successively carry one or more sheet-shaped manuscripts loaded in a layered state, to perform image reading.
2. Background
Conventionally two techniques, a fixed manuscript technique and a moving manuscript technique, are known for reading manuscript images.
In the fixed manuscript technique, the manuscript is fixed and an image information reading portion (optical unit) scans and reads it, which is therefore suitable for book-form manuscripts and thick-sheeted manuscripts. Furthermore, since the image information reading portion (optical unit) does the scanning, there is the advantage that reading precision is easy to increase.
In contrast to this, with the moving manuscript technique, the image information reading portion (optical unit) is fixed and reading is achieved by letting the manuscript do the scanning movement, and therefore there are the advantages that apparatus compactness can be achieved and the area occupied by an image forming apparatus or the like can be reduced. Furthermore, by placing manuscripts together in a manuscript tray, the manuscripts can be automatically taken out sheet by sheet and read, and therefore there are the large advantages that time and effort are reduced for a user and that a large amount of manuscripts can be read in a short time.
While the number of manuscripts that could be placed at one time in the manuscript tray with the moving manuscript technique was previously around 20 to 40 sheets, in recent years this has become around 100 sheets. Improved printing speeds, increased capacity of the memories in control portions that are provided in reading apparatuses and in which image data are temporarily stored, and improved control portion processing speeds have contributed to this.
However, when the number of sheets of manuscripts loaded in this way increases, there is a decreasing probability that the manuscripts (one job), once loaded, will be carried and read without any trouble. Furthermore, when the manuscript reading apparatus is used as a copying device incorporated into an image forming apparatus, the manuscript reading apparatus must also stop whenever there is trouble on the image forming apparatus side. And when this causes a manuscript to get caught up in the manuscript carry path, it is necessary to remove that manuscript.
On the other hand, there are apparatuses (see JP 2001-2256A for example) provided with a pickup roller that moves down from above one or more manuscripts loaded in the manuscript tray, then, upon contact, automatically takes out by its own rotation the top manuscript sheet by sheet and carries the manuscript in the carry path.
In this regard, the above-mentioned pickup roller is not always in contact with the top manuscript loaded in the manuscript tray, but is configured so as to come down and contact the top manuscript each time a manuscript is to be carried to the carry path. In this case, since the loaded amount of manuscripts loaded in the manuscript tray is not decided, there is a considerable difference in the distance by which the pickup roller comes down until it contacts the upper surface of the top manuscript loaded in the manuscript tray between when a small amount of manuscripts are loaded and when a large amount of manuscripts are loaded. For this reason, depending on differences in the descent velocity due to the driving force from the drive source when causing the pickup roller to descend and the pickup roller's own weight, the fewer manuscripts loaded in the manuscript tray, the larger the impact sound (contact sound) produced when contact is made with the upper surface of the manuscripts (i.e. the upper surface of the top manuscript among the manuscripts).
Furthermore, when a plurality of manuscripts are loaded in the manuscript tray, a clutch is provided to disconnect the pickup roller from the driving force of the drive source in order to intermittently carry the manuscripts by the rotation of the pickup roller in contact with the upper surface of the top manuscript, but this clutch disconnection-connection operation carried out between manuscripts causes drive power load fluctuation of the driving drive source. For this reason, a slight lag in the carry speed of the manuscript carried to the manuscript reading portion that reads manuscripts tends to be caused by the drive power load fluctuation, thus producing blurring in the reading of the manuscript in the manuscript reading portion.